Method of heat transfer



March 1, 1932. 1, ,.1 WAIT 1,847,542

METHOD OF HEAT TRANSFER Filed Dee. 15, 1924 INVENTOR ylfuf frm A TTORNEY Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE JUSTIN F. WAIT, OFNEW YORK, N. Y., ASSIGNOR TO SUN OIL COMPANY, 0F PHILADEL- PHIA,PENNSYLVANIA, A CORPORATION OF NEW JERSEY METHOD 0F HEAT TRANSFERApplication led December 13, 1924. Serial No. 755,708.

This invention relates to methods for the abstraction of heat from hightemperature fluids by means of a boiling metal held in thermal contacttherewith. It includes improvements and refinements which renderpossible commercial application of such theoretical operation. Somefeatures included in my previous applications of July 26, 1923, SerialNo. 654,054, which has matured into Patent No. 1,760,095, of May 22,1930, and December 21, 1922, Serial No. 608,347, are amplified inaccordance with more recent findings and others are furthersubstantiated by certain phases ofl this invention correlated therewith.

In view of the improved heat transfer which I have obtained with boilingmetals when in contact with metals having surfaces which they wet, Ihave further extended my equipment design to facilitate such wetting. Inpretreating the surfaces I have found it desirable to -increase thethickness of the wetted metal until it has sufficient strength to renderpossible complete elimination of' the steel parts previously used.

My invention, therefore, includes the use of commercially pure nickeland nickel alloys as for example nickel steel for use in those parts ofthe abstracting unit in contact with the high temperature fiuid and.which transfers heat therefrom. By limiting the use of the partscontaining an appreciable percentage of nickel to the main heat transfersurfaces, a substantial reduction in con'- struction cost is possible.Other metals for exampleplatinum which are wetted or form alloys whichare wetted may likewise be used. I have also discovered that ordinaryiron can be effectively wetted by liquid mercury, if the iron be firstplated with a substance, as for example, copper, with which the mercurywill form an amalgam of a nature which will be subsequently dissipatedin the body of the mercury. The formation and dissipation of the amalgampermits such intimate contact between the mercury and the iron as toyresult in wetting of the iron.

In addition to increase in heat transfer, the use of a wetted surfacegreatly precludes possibility of plugging of passages by oxides of theboiling metal or construction material or such other im urities as mightaccumulate. This invention urther relates to use of this principle inconnection with special design of surfaces and passages to insurecontinuous and highest rate of heat transfer. This matter is of utmostimportance in equipment involving metals, the value of which makesnecessary the use of passages and voids of maximum volume.

Plugging of the passages is further prevented and improved heat transferis further obtained b provision for more rapid recirculation o the metalwhereby vapor formed at the surfaces of the container is quickly sweptaway by unidirectional flow thereover of liquid metal, thus insuring amore constant wettinor of all portions of the heat transflerring suraces and preventing the formation of a relatively poorly conducting filmof vapor. During any given period, the amount of metallic liquid flowingpast a ortion of a heat transferring surface will e preferably more thantwo hundred times the amount of vapor evolved durin the same period fromthe surface. Accordingly, notwithstandino' the increase in volume of themetal attending vaporization, the liquid will be sufficient in amount tocleanse the surface from vapor. This rapid unidirectional flow of liquidcontrasts with the relatively local disturbances produced when liquidsare 0rdinarily heated, from which disturbances there results only arandom production of eddies and whirls of the liquid, inoperative toremove vapor films.

By further improving the recirculation between the metal walls and thefluid on one side and the boiling metal on the other side. Decidedimprovement may be obtained with a coating or plating of the walls incontact with the heated fluid such that the boiling metal would wet thesaid walls. As a further improvement, however, I have developed a meanswhich permits of even better and more permanent results. It consists ofgreatly increasing the thickness of the special coating until it issuiiciently heavy so that the non-wetting metal may be definitelyeliminated. For example, pure nickel tubes may be used thus yieldinghigh rate of heat transfer, and lessening the possibility of pluggingwith impurities.

An economical construction may be had by making only those parts,conducting heat from the hot iiuid to the boiling metal, of a metalwhich is wetted. Spacers and other` parts may be made of other metal andim-v proved in operation by a light plating of a wetting metal, althothe latter feature is not essential.

Vhile, perhaps, the common construction materials suitable for thisimprovement in operation of the abstractor are nickel and nickel alloyssuch as copper and iron containing alloys, other suitable materials maylikewise be used. T do not, therefore, limit my claims to metals oralloys containing nickel.

The use of a single special metal rather than a coating for the heattransfer surface insures continuity of operation and eliminatespossiblity of cracking or peeling by overheating and unequal expansionsinherent with a thin coat. The use of the recirculation principle,developed for maintaining uniform mixtures of alloys previouslydescribed, together With the use of a heavy plate or entire wall of thewetting metal, insures permanent and uniform operation.

Use of a naturally wetted surface not only gives better direct heattransfer results but also exerts a secondary influence on heat transferrate by greatly facilitating the Circulation rate across the surface.The reduction in coefficient of friction obtained when the surface iswetted thus also increases heat transfer and betters the heatabstraction etliciency. Circulation rates much in excess of thoseheretofore obtained may thus be obtained. By circulation rate is meantthe ratio of the total amount of metal passing a particular datum to theweight of that part thereof which is vaporized because of such passageduring the same period.

f Figs. l and 2, are sectional views showing several of the varioustypes considered in the development of the heat abstractor.

In each view, A represents acasing enclosing the hot fluid andcontaining a heat abstractor consisting of a wall B anda boiling metal Fthus held in thermal contact with the hot uid. C and D are the hot fluidinlet and outlet, respectively.

My invention includes the use of a metallic inner spacer to bothdecrease the mercury volume and to furnish definite passages .of suchdesign as to assist in the natural circulation such as would be had to amuch lesser degree in Fig. 1. T o this end, the spacer Gr is providedwith a central opening H, Figs. l and 2, and the slopes and passages sodesigned as to give definite unidirectional flow of the boiling liquidupward across the surface of B at such a rate that the vapor bubbles arequickly removed. I have found that with one or two hundred times theamount of metal vaporized sutlicient metal is circulated to insurepractically continuous wetting of the surface, thus eliminating theflashing tendency and obtaining the most i efficient heat transfer.Vapor is led to a condenser or to a point of use by an attachment to theoutlet E which may likewise be used for condensate return.

Such continuous treatment of the surface with a unidirectional flow ofthe metallic liquid is greatly assisted if the surfaces are pretreatedso as to eliminate absorbed gases and vapors and permit of actualContact between the wall and the metallic liquid.

A tendency to prevent Wet-ting of the surface exists in commercialinstallations because of the accumulation of impurities in the liquidmetal. A metallic oxide is frequently met and will coat the surfaces andoccupy space in chamber B, preventing proper wetting and' thereforelowering the heat transfer. To prevent this, the rapidly moving liquidwhich continuously wets the surface is greatly decreased in volume nearits upper surface and before it is started on its downward trip.

This important phase of my invention whereby l inflict differentialvelocities on the boiling metal has rendered commercial applicationspossible, as otherwise frequent cleaning of these passages would benecessary. This is a phenomenon not heretofore apparent and which ispeculiar only to operation of metallic liquids which are naturally verydense as compared with ordinary liquids, as water and oil.

Continuous wetting of the surface is therefore rendered positive andcertain by that phase of my invention illustrated in Fig. 2. Thisdiffers from Fig. 1 in that the volume occupied by F increases towardsthe top of the column of metallic liquid, thus reducing its velocity asit flows upward. Above the upper edge of spacer G the vertical velocityis at a minimum. The upper end of the channel H may be greatly increasedin the sectional area as shown at L to insure low velocity as the liquidassumes a downward motion. This lQw velocity permits the impurities torise to the surface due to the buoy- 13 ant effect of the heavy metallicliquid so that they will not be subsequently carried, due to the highvelocity of flow, downwardly int-o the chamber B. hey may be skimmedfrom the surface of the liquid when the apparatus is shut down. Thedecrease in upward velocity by increasing the area of the space occupiedby the metal F materially decreases splashing, thus affording asecondary preventative for downward passage of impurities. Baflies P andN are desirable for high velocities, the former guiding returning liquidto the central down-take section and preventing its return thru a regionof upflowing material, thus further extendingthe principle of uniiownecessary to efficient operation.

The application of a bonded coating of low melting metal such as lead isshown as Q in Fig. 2. This may cover all or part of the shell B and isin contact with parts of the liquid being heated.

One of the features necessary to good design is the fastening of thefingerlike chamber B at one end only, preferably the upper end, so thatthe opposite end is free for eX- pansion. The inner spacer G is likewisefastened at one point with reference to its longitudinal axis that itmay be free to expand. p

Obviously the number of fingers B may be multiplied.

These features are of major importance in heat abstractors embodied inthis invention because of the high temperature which give an unusualamount of expansion at a temperature approaching the weakening point ofthe metals used in the construction of the abstractor.

No cla-im is made herein to the apparatus illustrated and described, assuch forms the subject matter of an application filed as a divisionhereof, Serial No. 213,350, filed Aug. 16, 1927.

I claim:

1. The method of effecting heat transfer between a metal wall and aliquid in contact therewith, consisting of continuously wetting theliquid side of the wall by continuous circulation of the liquid at highupward velocity with decrease in velocity near the surface thereof.

2. The method of effecting heat transfer between a metal wall and aliquid in contact therewith, consisting of continuously wetting theliquid side of the wall by continuous circulation of the liquid at highupward velocity with decrease in velocity near the surface thereof andsubsequent reversal of vflow and downward flow of the liquid withgradual increase in velocity as it leaves the region near the surfacethereof.

In testimony whereof, I affix my signature.

JUSTIN F. WAIT.

